1. Field of the Invention
This invention relates to improvements in a continuously variable transmission of the type wherein a belt is passed on primary and secondary pulleys to transmit engine power from the primary pulley to the secondary pulley.
2. Description of the Prior Art
Conventional continuously variable transmission (CVT) of the type using a belt includes a primary pulley and a secondary pulley. An endless or loop-shaped belt is wound or passed on the primary and secondary pulleys. Each of the primary and secondary pulleys includes an axially fixed wheel counterpart and an axially movable wheel counterpart which are rotatable around a common axis. The fixed and movable wheel counterparts are respectively formed with generally frustoconical sheave surfaces which face each other to form a generally V-shaped pulley groove. Here, the primary and secondary pulleys are usually the same in surface roughness of the sheave surfaces of the fixed and movable wheel counterparts. The belt includes an endless steel belt portion or cylindrical ring. A plurality of plate-shaped steel elements are supported on the belt portion in a manner to be aligned along the periphery of the belt portion so that the adjacent ones are contactable with each other. The respective steel elements are engaged in the generally V-shaped grooves of the primary and secondary pulleys. Power is transmitted from the primary pulley to the secondary pulley under pushing force between the adjacent steel elements.
However, drawbacks have been encountered in the abovediscussed conventional continuously variable transmission. There is the possibility of relative sliding occurring between the steel elements engaged in the V-shaped groove and the sheave surfaces in the primary pulley. In case that the surface roughness of the sheave surfaces of the primary and secondary pulleys is higher (i.e., to make the sheave surfaces relatively rough), damage such as wear or breakaway of the surface portion tends to occur in the sheave surfaces when the relative slip is made between the steel elements and the sheave surface on the side of the primary pulley. This is problematic from the viewpoints of the durability of the primary pulley. On the contrary, in case that the surface roughness of the sheave surfaces of the primary and secondary pulleys is lower (i.e., to make the sheave surfaces relatively smooth), unnecessary processing such as grinding has been made also onto the side of the secondary pulley even though relative sliding does not occur between the steel elements and the sheave surfaces on the secondary pulley. This will shorten life of the grinder so as to be problematic from the viewpoint of production cost.